Smart Home - HEMS and haws

Or: the not-so smart part of the smart grid.

Thankful for the Yokohama Green Power project, part of Yokohama Smart City Project, we enjoy use of a 2011 version Home Energy Measurement System (HEMS). The diagram shows the energy management components surrounding the home gateway, the energy measurement unit is a separate unit near the utility breaker box. The HEMS was an option of the solar system we installed and is ours to use at 40% of its device cost subsidized, in return for sharing data over the course of 4 years with its supplier, Toshiba, and ultimately with the City of Yokohama. We have completed our solar year 3 with another fine harvest. According to the feed-in payments we get from TEPCO, the solar system performs 10% better than the forecast by the installer, Nitten Solar. (The HEMS reports even 10% on top of that, but that I discard as measurement uncertainty).

Do the stakeholders get their money's worth?

Do the stakeholders get their money's worth?

A quick answer: in terms of HEMS price/performance, no. With this his small wattmeter, a Revex ET30D costing about 2000 yen retail, in a month of plugging it in here and there to read device's power consumption, I have found energy savings worth a multiple of its cost in a year, so it has a quick payback. I was late to buy this kill-a-watt-like device only in winter 2013 because in the years before, I relied on the HEMS to show us where we may waste energy.

Not so much. I have found energy reductions about the same as this power meter but have yet to find anything coming close to offsetting the price of the HEMS, 250,000 yen (of which 100,000 yen were subsidized by the Yokohama Smart City Project, thank you very much).

Actual energy savings by HEMS: negative

Negative. About the best savings we could find was the 32W our TV combo with DVD player, Nintendo Wii and audio amp consume in standby. For decades, we had it on a power-disconnect switch already, like many other devices that do not need to be on. With a resident electrical engineer who measures and calculates standby losses as yearly sums, we may be not your typical household, leaving little room for additional savings from a HEMS. Your mileage may vary.

Power consumed, generated, sold, and used (8 channels) at the end of a mild day

Found the 32W one night, when checking the HEMS display on the iPad. The reading for our living room (labeled LDK - sorry, the software does not align the bars with the labels on an iPad) was not at its usual value. I then noticed the TV combo was left on standby, and switched it off, cutting power down to 4W, the mobile iPhone charging. Had we had the bad habit of not using the disconnect switch, we would have wasted some 7000 yen a year through keeping the TV combo on standby. A nice dinner for two. Financed by Negawatts. But then, we rarely forget to switch off, because the TV reminds us with its red pilot light.

Savings are negative in another more predictable way. The HEMS components themselves, data logger and home gateway (update: plus an iPod on its charger as a simple display unit) together consume some 19W according to the labels. On for 24h each day, for 8760h a year, costing us 5165 yen. Each. Year.

We have not much savings in sight to recover anything for this extra energy expense. How much could it be for an average user? About other participants in the Yokohama Green Power project, we hear once the novely wears off, after about half a year, they hardly ever again check the energy display.

Our HEMS is for Measurement

Energy monitor on iPhone

First off, ours is not a home energy MANAGEMENT system in the sense of the diagram above. Our HEMS that Toshiba calls feminity is set up for monitoring only. Going for energy management would involve replacing switches and outlets with remote controllable devices. In effect, it would add significantly to our electricity bill through the high standby consumption of the devices. When I last looked, a switch like the Toshiba BTL-3005AZ had 4W consumption. Replacing all our 32 switches at significant expense, we would be adding some 280W of standby. Being on for 24/7/365, these would be consuming 2500 kWh each year, costing some 60,000¥ before we could be saving anything off our 5700kWh annual consumption (this includes solar energy we did consume and not sell). We may be looking again at energy management when all switches, outlets and sensors consume less than 0.1W in standby, some makers are there already.

It Hems and Haws

In 2013 November and December, we could not calculate our monthly energy use because the summation was screwed up on Toshiba's server side. For two months, it showed absurd values, about five times over normal. Had we sold 17,985 kWh in a year as indicated at 48 yen per, we would have paid off the solar system in two years. Nope. The TEPCO eletric power consuption and feed-in invoice were normal. In January we reported to Toshiba, in early February they had fixed the database error. It sounded like were not the only ones affected.

HEMS no more

16V output for a device rated 12V?

On March 17, I noticed the Toshiba feminity home gateway lights were off. I am used to checking them often, because the unit frequently froze and needed to be restarted, every few weeks. First and easy thing to check: does it get power? Yes, the AC adapter 481206RO3CT puts out a bit over 16V.

But wait, on the gateway unit BTR-3005AZ it says 12V!

(Update: Toshiba confirmed this is normal, loaded with its rated 600mA, I measured the power supply outputs near 12V and consumes 11W) So the power supply going funky may have fried our gateway. From the start, a flaky supply voltage may have been a reason for the unit needing restart every few weeks. Countercheck with an AC adapter measured at 12.1V: the gateway remains dark.

Broken after 3 years and warranty is only one year. Asked Toshiba: a replacement feminity home gateway BTR-3005AZ costs 30,000 yen, plus 10,000 yen for the technician to set it up. No thank you, we have a smart home and cut our losses right here. With the help of the utility bill every month and the cheap wattage meter as needed, we will be fine, finding wasted energy and reducing overall consumption.

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Smart Home - HEMS and haws

Or: the not-so smart part of the smart grid.

Thankful for the Yokohama Green Power project, part of Yokohama Smart City Project, we enjoy use of a 2011 version Home Energy Measurement System (HEMS). The diagram shows the energy management components surrounding the home gateway, the energy measurement unit is a separate unit near the utility breaker box. The HEMS was an option of the solar system we installed and is ours to use at 40% of its device cost subsidized, in return for sharing data over the course of 4 years with its supplier, Toshiba, and ultimately with the City of Yokohama. We have completed our solar year 3 with another fine harvest. According to the feed-in payments we get from TEPCO, the solar system performs 10% better than the forecast by the installer, Nitten Solar. (The HEMS reports even 10% on top of that, but that I discard as measurement uncertainty).